It is important to account for manufacturing constraints in the design of a manufactured object. Traditionally, a designer of an object must anticipate manufacturing problems and must design the object keeping in mind the relevant manufacturing constraints.
For example, it is important in the design of an injection-molded object to consider whether the shape of the object provides sufficient “draft” to allow it to be properly extracted from a mold. An improperly designed object may get stuck in the mold and not extract properly. The shape of the molded object must be designed in a way that eliminates overhangs and undercuts and provides sufficient draft to allow the object to slide out of the mold. More specifically, the molded object may be required to have sufficient draft angle relative to: (1) a parting curve; and (2) a parting direction, where the parting curve indicates how the mold halves come together and the parting direction indicates the direction along which the mold halves are pulled apart during extraction of the object from the mold.
It is often difficult to change a model of an object to enforce a manufacturing constraint in the late stages of design. For example, it is often difficult to modify a boundary representation (BREP) model of an object to correct for inadequate draft. The difficulty lies with topology limitations of such models. If a BREP model needs to be modified in the late stages of design, only a very limited set of simple shape modifications may be made. Satisfactory modification of the model may be impossible if the model was not constructed carefully, for example, by using “draft-friendly” primitives (elementary geometric elements) in troublesome regions. Moreover, use of draft-friendly primitives may be aesthetically unsatisfactory or otherwise unacceptable for certain applications.
Furthermore, changing a design to comply with a manufacturing constraint generally requires expert knowledge about the manufacturing process—knowledge that the designer may not possess.
Traditional approaches typically require manual shape modifications in a multi-pass, iterative process based largely on expert knowledge. Modification may be made early in the design stage, where the burden is imposed on the designer to anticipate likely manufacturing problems, or during the manufacturing stage, where the cost of changing the design may be prohibitive.
Thus, there is a need for computer-aided design systems that provide tools for automatically modifying an arbitrarily-shaped model of an object to enforce compliance with manufacturing constraints. A technique is needed that allows a designer to correct a model after completion of the initial design, but before final approval and/or before manufacturing of the designed object.